Old autopilot and loran c vs. gps

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J.R. Good

Member
Joined
Dec 13, 2020
Messages
22
Vessel Name
Chesapeake
Vessel Make
Grand Banks 36 CL
Hi Folks,

I recently found a NOS Cetec Benmar Compu-course 220 that I will be installing on my boat. The input for auto-trac is set up for 2 wire Loran C data. Can this unit be made to work with the GPS signal running my OpenCPN nav software? I tried contacting the gentleman at Benmar Marine but the line is not in service anymore and the website says "temporarily closed". Let's hope it's just temporary!

TIA,

Randy Good
GB36-231
 
Probably not.
Every electronics has a stage where the newer stuff will not work work older tech. On the forum people have chart plotters only a few years old, obsolete, no upgrades.
 
Hi Folks,

I recently found a NOS Cetec Benmar Compu-course 220 that I will be installing on my boat. The input for auto-trac is set up for 2 wire Loran C data. Can this unit be made to work with the GPS signal running my OpenCPN nav software? I tried contacting the gentleman at Benmar Marine but the line is not in service anymore and the website says "temporarily closed". Let's hope it's just temporary!

TIA,

Randy Good
GB36-231

It depends.

If the output from Loran C that the autopilot is looking for is NEMA 0183, then depending on your GPS or MFD, you may be able to output 0183 to your autopilot. Do you have the manual for the autopilot? If not try Google searching for it.

Ted
 
Benmar did offer an upgrade to use GPS. The APU was sent back to them for the necessary upgrade.



Upgrades
 
I know nothing about this particular AP, nor about the standards for Loran communications between devices. But unless the AP has been converted to accept standard NMEA GPS data as described above, I seriously doubt it will work.
 
Thanks for the replies! The manual does state that the APU is set up to receive nmea 0183, so there's that anyway. I have a lot more reading to do...
 
Last edited:
Thanks for the replies! The manual does state that the APU is set up to receive nmea 0813, so there's that anyway. I have a lot more reading to do...

Your manual for your GPS or MFD should have information on the 4 wires for 0183. One pair listens; the other pair talks. You will need to connect the talking pair to your autopilot.

Ted
 
Your manual for your GPS or MFD should have information on the 4 wires for 0183. One pair listens; the other pair talks. You will need to connect the talking pair to your autopilot.

Ted

So I will need to get an 0183 GPS antenna has more than just a coax cable, yes?
 
So I will need to get an 0183 GPS antenna has more than just a coax cable, yes?

What does this antenna hook to?

You need a device, such as a MFD (multi function display) or GPS unit. In simple terms, you need a device with a screen that you can put a waypoint on and have that unit navigate to it. Most of these display units have an output cable that includes the 0183 wires. So it really doesn't matter how the GPS antenna is wired to the unit. It's the unit that outputs the information to the autopilot.

Ted
 
What does this antenna hook to?

You need a device, such as a MFD (multi function display) or GPS unit. In simple terms, you need a device with a screen that you can put a waypoint on and have that unit navigate to it. Most of these display units have an output cable that includes the 0183 wires. So it really doesn't matter how the GPS antenna is wired to the unit. It's the unit that outputs the information to the autopilot.

Ted

I have 2 stand alone Garmin GPS 220 units that show me SOG and position, one at each helm. They are not used for plotting. For Chart plotting I have OpenCPN installed on a Mac Mini running TFT displays. All that works great, but I am (obviously) at the shallow end of the learning curve in understanding how to get what to talk and listen to what so the AP will execute plotted waypoint heading changes that are on OpenCPN.
Thanks for your patience!!
 
So I will need to get an 0183 GPS antenna has more than just a coax cable, yes?
You're going to need something after the coax and before the autopilot. The signal coming out of the coax is raw GPS data. You're autopilot needs NMEA message strings. The autopilot of your vintage likely a "dumb" autopilot. It won't process the raw GPS data to create NMEA scentences. You'll need to look at the documentation to learn what NMEA messages the AP needs. There are members here who know far more than I. It will help them if you can list all of your nav devices.

What I can offer is some help sorting out the two talker wires and the NMEA scentences being sent to the autopilot from what ever you have. You are about to enter the twilight zone of serial data. The two talker wires are polarity sensitive. The autopilot may need certain NMEA messages. It's helpful to be able to "see" those messages. Here is the method I have used. On a laptop with Rose Point's Coastal Explorer hook the NMEA talkers to the laptop via a serial to USB port. Ask CE to auto configure nav devices and open the troubleshooting window. If you see nothing or garbage then reverse the talker wires. You should now see NMEA messages.

The reason I suggest CE is because it has in my experience the best ability to auto find and configure nav input. If the app cannot auto configure you'll need to know the port ID# and other things. This can be a frustrating exercise in trial and error. If you don't already own CE then download a trial version. It used to be fully functional and run for 10 days. I haven't had to play that game in a long time, hopefully they still offer a fully functional trial.

You'll soon learn why many favor the newer network protocols.
 
I see your and O C Diver's posts after I posted. OpenCPN should be able to drive your autopilot. You'll still need a USB to serial converter to get from OpenCPN to the autopilot. Now it's a simple polarity test. Try it one way, if it works great. If not reverse the wires.
 
I have 2 stand alone Garmin GPS 220 units that show me SOG and position, one at each helm. They are not used for plotting. For Chart plotting I have OpenCPN installed on a Mac Mini running TFT displays. All that works great, but I am (obviously) at the shallow end of the learning curve in understanding how to get what to talk and listen to what so the AP will execute plotted waypoint heading changes that are on OpenCPN.
Thanks for your patience!!

Is this the unit you have?

https://www.garmin.com/en-US/p/6416#specs

Ted
 
Oh man, typo. 120, not 220. They are older models, each with their own antenna. The computer uses a puck antenna.
 
Like this GlobalSat BU-353-S4 USB GPS Receiver
 
A bit more, I haven't had enough coffee yet.

Your GPS unit may be able to issue autopilot steering commands on a NMEA 0183 network. If so you can go straight to the autopilot. However you won't have the functionality a plotter like OpenCPN offers to create and store waypoints and routes while working on a chart.

If you don't already have a heading sensor and your autopilot requires heading then you'll need to add that as well. I'd put the heading sensor's data into OpenCPN then feed that to the autopilot.

As I said up thread its been a long time since I worked with NMEA 0183. At that time I used gear by Noland Engineering to gather multiple NMEA 0813 messages, buffer them and output to things like autopilots.
 
Oh man, typo. 120, not 220. They are older models, each with their own antenna. The computer uses a puck antenna.

Ok, so bad news and good news.

The bad news is that they don't have map data (which you already know).

The good news is that they have 0183 input and output. So, if you want to test that your autopilot will run off of 0183, you can wire it to the autopilot, take the boat out, enter a waypoint (GPS position [hopefully in navigable water :rolleyes:]), and see if the autopilot takes you there. Obviously, interfacing the autopilot to your OpenCPN would be a better feature choice, but this lets you prove the autopilot will work without investing $.

Ted
 
Thanks very much Ted:thumb: I may have access to a Garmin 220, but I'll start with seeing if the signal even works with what I have.
I really appreciate the help.
 
A bit more, I haven't had enough coffee yet.

Your GPS unit may be able to issue autopilot steering commands on a NMEA 0183 network. If so you can go straight to the autopilot. However you won't have the functionality a plotter like OpenCPN offers to create and store waypoints and routes while working on a chart.

If you don't already have a heading sensor and your autopilot requires heading then you'll need to add that as well. I'd put the heading sensor's data into OpenCPN then feed that to the autopilot.

As I said up thread its been a long time since I worked with NMEA 0183. At that time I used gear by Noland Engineering to gather multiple NMEA 0813 messages, buffer them and output to things like autopilots.

Thanks for this info and help! It may all work out yet without having a great deal on a new old stock AP cost more than it's worth to get working with waypoints.
 
Probably it will work if it's 0183. The GPS should send the same info as the loran- range and bearing to waypoint, and cross track error. These two are what the pilot needs in NAV mode.
 
Probably it will work if it's 0183. The GPS should send the same info as the loran- range and bearing to waypoint, and cross track error. These two are what the pilot needs in NAV mode.

I'm also trying to figure out how to actually wire up the connection between the 0183 data as shown on my nav software screen and the AP. If I connect one of these (DTECH RS232 to RS485 / RS422 Serial Communication Data Converter Adapter) to the data port on the Mac Mini that runs my nav software (OpenCPN), will that work? Is there a way to tell OpenCPN to output that data as well as use it for charting and vessel position?

Thanks very much for the help!
 
I'm also trying to figure out how to actually wire up the connection between the 0183 data as shown on my nav software screen and the AP. If I connect one of these (DTECH RS232 to RS485 / RS422 Serial Communication Data Converter Adapter) to the data port on the Mac Mini that runs my nav software (OpenCPN), will that work? Is there a way to tell OpenCPN to output that data as well as use it for charting and vessel position?

Thanks very much for the help!
If I understand your system and questions you have OpenCPN functioning correctly with data from your Garmin GPS. You want to use a Serial DTECH Communications Data Converter Adapter to get data from OpenCPN to the AP.

I'll tackle the "easy" part first. Sending AP data from OpenCPN. Open Settings/Connections/Add Connection and set up a new connection. Some of the setup is simple, some not. Here's a full discussion Route to Autopilot OpenCPN The most challenging part for me has always been getting the data port correct. Sorry, can't help with that, it's going to be system dependent. Consult your AP manual to see which NMEA sentences it needs to function.

Next the hardware. There will be two connections to make. The first is Mac Mini to the converter. Then converter to AP. I can't help with Mac Mini to the converter because I don't know diddly about the Mac Mini.

From the converter to the AP is sort of straight forward. I'd first try RS422 because most older NMEA 0183 devices use that protocol. Your AP manual should tell you where to connect the two wires from the converter. It should also tell you the serial protocol so you know for certain if RS422 is needed. Remember when you test this the two serial data wires are polarity sensitive. There is no risk to the equipment getting the reversed but it won't work. There are a number of good resources on the net on how to troubleshoot and test NMEA 0183 data. This link Testing NMEA0183 might be a good place for you to start. The author describes a simple test using an LED to determine if there is a live connection and if polarity is correct. I've used this in the past with good success.

If you are not successful at this point one you may want to "see" the data coming into the AP. This is going to require additional hardware and software. Something that you can connect to the two wires you would normally connect to the AP and view the NMEA sentences. But that's another NMEA / serial data nightmare in itself. However here's a link to a good discussion on NMEA 0183 sentences. You don't need to read the whole thing. You'll be looking for lines of text that start with $ and then a 3 character sentence description then the data. If you see the sentences the AP needs and recognizable alpha numeric characters then all is probably good. If you see garbage then certainly it is not good and you need to check all of your connections. To get an idea of what a healthy NMEA sentence looks like with OpenCPN running and recieving data from the GPS open Settings/Connections and tick the Show NMEA Debug Window box. A stream of proper NMEA sentences will display.

You've set yourself a challenge. Connecting new to old to really old tech. It can be done but and you'll learn a lot in the process.
 
If I understand your system and questions you have OpenCPN functioning correctly with data from your Garmin GPS. You want to use a Serial DTECH Communications Data Converter Adapter to get data from OpenCPN to the AP.

I'll tackle the "easy" part first. Sending AP data from OpenCPN. Open Settings/Connections/Add Connection and set up a new connection. Some of the setup is simple, some not. Here's a full discussion Route to Autopilot OpenCPN The most challenging part for me has always been getting the data port correct. Sorry, can't help with that, it's going to be system dependent. Consult your AP manual to see which NMEA sentences it needs to function.

Next the hardware. There will be two connections to make. The first is Mac Mini to the converter. Then converter to AP. I can't help with Mac Mini to the converter because I don't know diddly about the Mac Mini.

From the converter to the AP is sort of straight forward. I'd first try RS422 because most older NMEA 0183 devices use that protocol. Your AP manual should tell you where to connect the two wires from the converter. It should also tell you the serial protocol so you know for certain if RS422 is needed. Remember when you test this the two serial data wires are polarity sensitive. There is no risk to the equipment getting the reversed but it won't work. There are a number of good resources on the net on how to troubleshoot and test NMEA 0183 data. This link Testing NMEA0183 might be a good place for you to start. The author describes a simple test using an LED to determine if there is a live connection and if polarity is correct. I've used this in the past with good success.

If you are not successful at this point one you may want to "see" the data coming into the AP. This is going to require additional hardware and software. Something that you can connect to the two wires you would normally connect to the AP and view the NMEA sentences. But that's another NMEA / serial data nightmare in itself. However here's a link to a good discussion on NMEA 0183 sentences. You don't need to read the whole thing. You'll be looking for lines of text that start with $ and then a 3 character sentence description then the data. If you see the sentences the AP needs and recognizable alpha numeric characters then all is probably good. If you see garbage then certainly it is not good and you need to check all of your connections. To get an idea of what a healthy NMEA sentence looks like with OpenCPN running and recieving data from the GPS open Settings/Connections and tick the Show NMEA Debug Window box. A stream of proper NMEA sentences will display.

You've set yourself a challenge. Connecting new to old to really old tech. It can be done but and you'll learn a lot in the process.

Thanks to all the help from this Forum I've learned two main things: The magnitude of how much I didn't know I didn't know, and it looks possible anyway!

The OpenCPN is functioning without a GPS device, just a GPS puck antenna plugged directly into a USB port on the Mac. The Mac has a serial data port that would accept one end of the converter/adapter hardware and the AP 0183 inputs to the other end. I'll wade into the OpenCPN manuals and try to get a better understanding of how to set up the software to play nice with the AP. I'll try that first, and hope then it's nothing more complicated than getting the polarity to the AP right.

I'm glad to be able to have done all my own boat carpentry, house wiring and plumbing and diesel work. That's why I love having an old wood boat. But this Nav stuff is way beyond me. I stopped working on my own cars when they did away with carburetors, distributer caps and points. :oldman:

Thanks again, huge help!
 
The OpenCPN is functioning without a GPS device, just a GPS puck antenna plugged directly into a USB port on the Mac. The Mac has a serial data port that would accept one end of the converter/adapter hardware and the AP 0183 inputs to the other end.
Again, if I understand your system. OpenCPN is running fine with the puc. No 0183 input needed to the Mac. 0183 output is needed to the AP provided by OpenCPN. It looks like the converter will do that after you configure OpenCPN.

One caution. RS422 RS232 are very sensitive to noise. Use shielded cable if you can find it. Route it away from wiring that can induce noise.
 
Shielded from the converter to the AP right? I can do that.
 

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